Furnace



H. C. RENTSCHLER Jan. 8 1924.

FURNACE Filed D60. 15

R O T N E V m I WITNESSES:

lama 0. fienfschlert ATTORNEY Y Patented Jan. 8, 1924.

UNITED STATES PATENT OFFICE.

HARVEY C. RENTSOHLER, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE LAMP OOMPANY, A CORPORATION OF PENNSYLVANIA.

FURNACE.

Application filed December 13, 1920. Serial No. 430,118.

To all whom it may concern."

Be it known that I, HARVEY C. RENT- scrimin, a citizen of the United States, and

a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Furnaces, of which the following is a specification.

This invention relates to furnaces, more especially to electric furnaces utilizing induced currents to produce heating effects.

Several types of electrically heated furnaces have been proposed. Among these was one in which an evacuated container was provided with a graphite or carbon tube within which was placed a graphite coil through which alternating current was passed. A crucible or other object to be heated was placed within the graphite tube, out of contact with the coil, and the heat radiated from the coil was transmitted to the crucible.

Another furnace of the electrical type, and one commonly used for the production 2 of steel, consisted in a set of primary windings similar to those used in transformers, the secondary of the furnace bein a trough or similar shaped circular mem er. Current was passed through the primary of the furnace which induced secondary currents Fin the metal placed in the trough secondary, 3 thus melting the metal and holding it at an \elevatcd" temperature to effect purification fthereof.

In furnaces of the above defined types, the primary consideration was to obtain a sufficient amount of heating for the purpose for which they were designed. However, such furnaces are limited in practice, by their 40 construction, to relatively low temperatures and they have been found impractical for the production of temperatures materially above 1500 (l, and generally in the neigh borhood of 3000 (1., especially in a vacuum.

The heat losses in the first-mentioned furnace were very great, the heat generated by the resistance of the coil being transmitted in all directions, and not necessarily con entinted upon the object to be heated. To

more perfectly confine the heat, shielding members were formed about the heating coil, but even such devices did not cause a large proportion of the generated heat to penetrate into the crucible. Much volatile matter was given off by the heated coils, male ing it difficult to maintain a vacuum and to prevent contamination of the materialbeing heated. t

In the second type of. furnace, heat in the secondary is produced by induction from an alternating current in a primary through interlinkage of the primary and secondary by a magnetic core. In this type of furnace, because of the presence of large quantities of magnetic materials used in the core, it is impossible to practice any heat treatments of materials which are readily conterminated when brought in contact with deleterious substances. During the heating of the material the large quantities of iron or other magnetic material slowly gives off occluded gases and these gases readily contaminate the metal undergoing treatment.

Although a furnace of the type specified was capable of melting iron and steel rather readily, it was found impractical to treatmaterials which required considerably higher temperatures, especially where high vacuum was necessary.

The furnace. which I have devised is adapted to produce higher temperatures (from 1500 C. to 3000 C. and even higher,) in a high vacuum, in a very simple manner with. reat efficiency. It is among the objccts of the present invention to provide a furnace structure which is simple in construction and easy to manipulate, and one which is capable of providing high temperatures with a minimum expenditure of electrical energy.

In practising my invention, I provide a chamber, which is preferably evacuated, and form therein a coil connected to a source of high-frequency current. Within the coil I place a crucible of metal or an equivalent structure,-such as a metal disk or disks, the crucible or other device being closely spaced from the coil. I generally form the. coil with closely spaced loops.

In a furnace of this character, high-fre quency current is passed through the coil which constitutes the primary of the circuit, the crucible or other device being the secondary. The induced currents are of great lOO magnitude and produce intense heating of the contents of the crucible. There are practically no radiation losses since the crucible is almost entirely surrounded by the prin'lary coil which will intercept most of the radiations from the crucible and reflect a ltll'fl portion of them back again.

M furnace has given excellent results and. by means thereof, I have been enabled to sinter and melt various metals which have hitherto resisted all heat tr atments of this character. For instance, I have placed powdered uranium, thorium, vanadium, titanium, tungsten, Zirconium, and others of the rare metals within the crucible and upon beating them for short periods of time, have produced coherent metal deposits which are, in most cases, non-porous and are entirely metallic in all their properties.

So far as I am aware, no prior method, relying solely on a heat treatment of the rare metals or their alloys, has produced therefrom a pure coherent metallic body homogenous throughout.

1 am aware, however, that high frequency currents have been utilized for heating a mass of material directly without the interposition of a magnetic body, but so far as I have been informed, no one has discovered that such currents, could be safely carried in a coil having its turns lying adjacent each other, when disposed in a vacuum or an inert environmentof low pressure, as it was believed that if this were attempted, the coil would be disintegrated by arcing or electron emission. The applicant has discovered that by evacuating the vessel in which the primary is located that arcing is limited to such an extent that the life of the coil is not materially affected.

in the accompanying drawings forming a part hereof and which illustrate several em-- bodiments of my invention,

Fig. 1 is a view, in elevation, of one form of my furnace, some parts being shown in section;

Fig. 2 is an enlarged elevational View of the heating element shown in Fig. 1;

Fig. 3 is a similar View of a slightly different form of heating element;

Fig. l is a cross-sectional view'on the line IVIV of Fig. 1, and

Fig. is an elevational View, some parts being shown in section, of a slightly olifieren form of furnace. 1

A hollow body orchamber 1' of anysuit able shape and material, prcferablyglass, is

provided with a tubefl which may be connected to a source of high vacuum, such as a diffusion pump. Thehollow body is usually of dome or bulb shape, and I generally prefer to construct the same of glass or other transparent material. The lower end 3 of chamber 1 is provided with a stopper. 4 which is closely fitted therein and is sealed in by any suitable means, such as a special scaling wax. when the furnace is in operation.

Vi'ii'cs and (l are fused into stopper l, the ends of said wires being secured to a closely wound coil T centrally located within the chamber 1. The coil '4' will be termed hereinafter lbc induction coil or the primury. This coil has its turns lying closely adjacent each other and thus forms in cliect a hcilow body or wall which c unpletely surrounds the secondary and thereby rcl'lects any radiant heat given oli' by the secondary. A metal support 8, insulated from wires 5 and t3 and coil T, is also fused into stopper 4:, and a crucible 9 is secured to the upper end thereof, the crucible being entirely contained within the coil 7 and closely spaced therefrom. Material to be heated is placed within the crucible. 'lhe crucible 9 and the material 10 may constitute the resistor or secondary or either of these elements taken alone may perform that function.

An interrupter 11, consisting of a scaled, hollow, evacuated body portion 12 into the bottom of which is fused a metal contact member 13 connected to wire 5 by lead 14, is provided. A receptacle 15 is placed in the bottom of the interrupter, the receptacle and the space 16 between the two bodies being filled with mercury. The mercury within the receptacle 15 and that between the receptacle 15 and the interrupter comprise two electrodes between which the arc plays. A contact member 17 is secured in the bottom of receptacle 15, and a lead wire 18 connects the same to lead 6. A glass or other insulating medium surrounds that portion of wire 18 which is not submerged in the mercury 20 in receptacle 15.

Induction coil 7 in series with a capacitance device 22 is connected in circuit 5-6 in parallel, said circuit being closed by secondary coil 23 of transformer 24 connected to a suitable source of alternating current, such as a 110 volt, 6O cycle current.

A source of direct current 25 maybe provided in the circuit with means 26, such as a switch, to allow the same to be inserted into, or disconnected from, the circuit.

Instead of utilizing a crucible 9 for holding material 10 to be heated, 1 may provide a, disk 27, as shown in Fig. 3, and secure the same tometal support 8. "lihe material 10, int-he form of a disk or pellet, is placed thereon and another disk 28 thereover. In

The device thus far described furnishes an admirable heater which has its induction coil and the resistor located entirely within a closed chamber which may be evacuated 0r contaln an mert environment. Furthermore, the heating of the resistor, as well as stituting the secondary of the circuit.

an extremely short time, usually a very few the material supported thereby, may be carried on Without the interposition of magnetic material or by the interlinkage of the induction coil or inductor element with the resistor by transformer magnetic material such as iron and the like. By the close magnetic coupling of the primary coil and the resistor, a better heating efiect-may be had as the electrical energy is practically all converted into thermal energy. The heat is further conserved by arranging the coils of the primary closely adjacent each other and thus reflecting radiant heat from the resistor toward that element. In addition, the radiant heat from the primary coil is partly directed toward the resistor. These combined features enables me to secure much higher temperatures with the same expenditure of electrical energy than has hitherto been possible.

The embodiment of my furnace shown in Fig. 5 is similar to that shown in Fig. 1, the coil 7 being permanently fixed in one end of the chamber 1, and only the crucible 9 or other device secured to the stopper 4, which is removable.

In order to produce sintered metallic tungsten in my furnace, I proceed as follows: Powdered tungsten, which may be obtained by any of a number of methods, is compressed in a suitable mold to the desired shape and placed either in crucible 9 or upon disk 27 carried by plug or stopper at and placed in the furnace chamber. The stopper is sealed into position and the furnace evacuated through tube 2.

Switch 26 is closed, causing current. to flow through coil 7 heating crucible 9 or disk 27 by radiation. This causes any oceluded gases in the material to be expelled and drawn out through tube '2. Switch 26 is then opened, cutting off the direct current, and the alternating current circuit is closed, causing current to flow through transformer 24, interrupter 11, and coil 7. By this means, I provide a relatively high voltage and a high frequency. I have used with good success 7000 volts at a frequency of 100,000 cycles.

The rapid pulsations of current in primary coil 7 cause intense heating of crucible 9 or of disks 2'? and 28 and of material 10 by induction, the crucible and material coIn minutes, the very refractory powdered metal is sintered, forming a coherent metallic button of tungsten which may be removed and Worked in any desired manner.

My construction provides a furnace in which the heating .is very rapid and intense, practically all the energy of the highfrequency current being concentrated upon the material being heated. My 1nterrupter, which provides parallel edgesof considerable length between the two bodies 16 and 20 of mercury for the purpose of distributing the arcing discharge, is very effective in producing a high-frequency current.

I am aware that induction heating in a vacuum has been attempted before and that furnaces have been constructed in which an article to be heated was secured in an evacuated vessel, the article constituting the secondary of an induction device. The primary coil was wound on the outside of the evacuated vessel. My invention is distinguished from such structures in that both the primary and the secondary are placed within the vessel in close relation to each other. By providing this arrangement, I concentrate the heating effects in a very small area and utilize a large proportion of the energy for the useful heating.

My furnace is very well adapted to the production of pure metals at high temperatures. The metals may be produced either from the powdered elements or directly from compounds of the elements by chemical reactions. Nor is my furnace limited to the'production of metals since I have been enabled to produce alloys, in exactly the same manner as that used in the production of the pure metals.

My furnace is so eflicient that the chamber 1 iscool at practically all times, and it is never necessary to use artificial cooling, as was the case in prior structures.

Although I use a high-frequency current in my heating coil, the individual loops of which are close together, I have found no difiiculty on account of electrical discharge between adjacent loops. In fact, the electrical energy flowing through the coil is so completely transformed into heat energy in the secondary that the primary coil rarely, if ever, becomes hotter than a red heat.

By providing a relatively large chamber, generally of lass, I am enabled to prevent material heating of the same so that it remains cool at all times. Since the container is cool, it is a comparatively simple matter to maintain a vacuum therein, because no gases can defuse through cold glass. in an arrangement of this kind, the material. being treated may be at amuch higher term perature than the coil through which the gases from metals for the purpose of analysis, for the formation of alloys Where precaution must be taken to avoid contamination thereof, and for conducting high-temperature reactions.

Although I have described several embodiments of my invention. it is to be understood that it. is not limited to the details of construction set forth but various changes may be made within the scope thereof. For instance, the chamber 1 constituting the walls of the furnace need not necesarily be of glass but may be constructed of any suitable refrectory material of a metallic or non-metallic nature.

l have described the preliminary heating of the material by direct current but it is obvious that low-frequency alternating current passed through coil 7 or alternating current passed through a coil surrounding chamber 1 or other suitable preliminary-heating means may be substituted therefor. These and other changes Which Will be obvious to those skilled in the art may be made in the details of construction of my furnace which I desire to cover broadly by the claims appended hereto.

1 claim as my invention: 7

1. A. furnace comprising a chamber having an inert environment. an induction'coil Within said chamber and adapted to heat a resistor and means for passing high-frequency current through said coil.

2. it furnace comprising an evacuated chamber, an induction coil therein adapted to heat a resistor and means for passing high-frequency current through said coil.

till) 3. A furnace comprising an evacuated chamber, an induction coil therein, a resistor adapted to be inductively heated thereby and means for passing high frequency-ourrent through said coil. e

4s. A furnace comprising an evacuated chamber, a hollow induction coil therein, a resistor Within said coil and adapted to be inductively heated thereby and meansfor passing high-frequency current through said coil.

5. A furnace comprising an evacuated chamber, a hollow induction coil-therein and having its turns lying closely adjacent each other, a resistor Within said coil and adapted to be inductively heated'thereby and means for passinghigh-fiequency cur rent through said coil. 1

ti. A. furnace comprising" a chamber hav ing an inert environment, an'induction coil Within said chamber, a resistor adjacent said coil, means for passing hi gh-frequency current through said coil, the arrangement of the parts being such that theelectri'c' energy athigh frequency is. inductively transferred from the coil to theresistor and trans formed into heat therein Without the interposition of magnetic material.

7. A furnace comprising a chamber having an inert environment, an induction coil Within said chamber acting as the primary, aresistcr Within said coil acting as the secondary, means for passing high-frequeneycurrent through said coil, whereby the electric energy at high frequency is inductivelv transferred from the coil to the resistorand transformed into heat therein Without the interposition of magnetic material.

' 8. A. furnace comprising a chamber, an induction coil therein, said coil having its turns closely adjacent each other so as to form in effect a cylindrical wall, a resistor Within said coil and spaced therefrom, means for passing high-frequency current through said coil and an inert environment- Within said chamber forming a non-magnetic path between said coil and said resistor.

'9. A. furnace comprising a hermetically sealed chamber, an induction element therein, a resistor element in close proximity thereto, leading-in Wires extending from said induction element to a point Without said chamber, a source of high-frequency current supply connected to said leading-in Wires, said induction element being free from transformer magnetic core interlinkage with said resistor element.

10. A furnace comprising a chamber, an induction element therein, resistor in close proximity to said element and adapted to be heated inductively and reflectively thereby and means for passing higlnfrequency current through said induction element.

11. A furnace comprisng; a chamber, an

induction element having a series of turns,

of Wire lying closely adjacent each other so as to form in effect a cylindrical wall, a resistor Within said induction element, said resistor adapted to be heated inductively and by radiant heat reflected by said induction element.

'12. A furnace comprising a chamber, an inductionelement having a series of turned of Wire lying closely adjacent each other so as to form in effect a cylindrical Wall, a TGSlStOT'WltlllH said induction element, said resistonadapted to be heated inductively' and by radiant heat from and reflected by said induction element.

' 13. A furnace comprising a chamber, an induction element and a resistor therein,

means for passing high-frequency current through said element and means for maintaining' a vacuum Within said chamber.

14-. A furnace comprising a chamber, an induction coil and a resistor Within said chamber, means for passinghigh-frequency current through said coil and means for maintaining'a vacuum Within said chamber. 15'. A. furnace comprising a chamber, a coil therein, means in proximit to said coil for holding material to be heated, said coil being adapted to heat said means free from interlinkage of transformer iron, a highfrequcncy source for said coil including an alternating current source, an interrupter and a condenser. said interrupter comprising a plurality of chambers containing mercury and so constructed as to present relatively long parallel edges between the mercury bodies.

16. A furnace comprising a chamber, a coil therein, means in proximity to said coil for holding material to be heated, said coil being free from interlinkage of transformer iron and adapted to inductively heat said means, a high-frequency current source tor said coil including an alternating current source, an interrupter and a condenser.

17. A furnace comprising a chamber, a coil therein, means in proximity to said coil for holding material to be heated, said coil being free from interlinkage of transformer iron and adapted to inductively heat said means and material, a high-frequency cur rent source for said coil including an alternating current supply, an interrupter and a condenser, said interrupter comprising inner and outer chambers, the inner chamber being of less height than the outer chamber, mercury electrodes within each chamber and spaced from the upper edge of the inner chamber, conductors for connecting the said electrodes with the circuit.

18. A furnace comprising a chamber, a coil therein, means in proximity to said coil for holding material to be heated. said coil being free from interlinkage of transformer iron and adapted to inductively heat said material, means for maintaining a vacuum in said chamber, a high-frequency current source for-said coil including an alternating current supply, an interrupter and a con denser, said interrupter comprising inner and outer chambers. the inner chamber being of less height than the outer chamber, mercury electrodes within each chamber and spaced from the upper edge of the inner chamber, a conductor for connecting the electrode in the outer container with said condenser and a conductor for connecting the electrode in the inner container with said coil, said condenser being also con nected with said coil.

19. A furnace comprising a chamber, a coil therein, means in proximity to said coil for holding material to be heated, said coil being free from interlinkage of transformer iron and adapted to inductively heat said material, means for maintaining a vacuum in said chamber, a high-frequency current source for said coil including an alternating current supply, an interrupter and a condenser, said lnterrupter comprising inner and outer chambers, the inner chamber being of less height than the outer chamber, mercury electrodes within each chamber and spaced from the upper edge of the inner chamber, a conductor for connecting the electrode in the inner container with said condenser and a conductor for connecting the electrode in the outer contaimr with said coil, said condenser being also connected with said coil.

20. .r furnace comprising a chamber, an induction coil therein, a resistor adapted to be inductively heated thereby. means for preliminarily effecting the heating of said resistor and means for passing high-irequency current through said coil.

21. A furnace comprising a chamber, a resistor therein, a coil adapted to inductively and radiantly heat said resistor, means for preliminarily heating said coil, means for passing high-frequency current through said coil and means for maintaining a vacuum in said chamber.

22. The method of heating which comprises subjecting a material to high-trequency induction developed within a closed container.

23. The method of heating which comprises subjecting a material to high-trequency induction developed within a closed container and in the presence of an inert environment.

2 The method of heating which comprises subjecting a material readily oxidizable in air to high-frequency induction developed within a closed container and in the presence of an inert environment.

25. The method prises subjecting a quency induction developed vacuum.

26. The method of heating which comprises subjecting a material to high-frequency induction and radiant heat reflection.

27. The method of heating which comprises subjecting a material to high-fro quency induction, direct heat radiation and radiant heat reflection.

28. The method of obtaining a high temperature, which consists in developing a high-frequency induction within a high vacuum device.

29. The method of transferring electric energy into a mass so as to become thermal energy therein, which consists in circulating high-frequency currents in inductive relation to the mass, tree from interlinkage of a transformer magnetic circuit with the electrio circuit and conducting such treatment in an inert environment.

30. The method of applying energy by electromagnetic induction to be converted into heat within a removable resistor mass, which consists in inducing high-frequency currents within the resistor, free from intermaterial to high-frewithin a of heating which comlinkage of a transformer magnetic circuit with the electric circuit and conducting such treatment in a high Vacuum.

31. The method of furnace heating, which i consists in inducing electric current flow within a mass of material directly from high-frequency electric current flow outside the mass, but enclosed therewith in an envelope containing an inert environment, as

distii'iguished from linking the material in former magnetic circuit. 32. The method of turnace heating WlllCh consists in inducing electric current flow the mass and the outside current by transwithin a mass of material directly from.

higlrirequency current flow outside the mass, as distinguished from linking the material in the mass and the outside current by transformer magnetic circuit, and additionally heating said mass by reflected radiant heat. 5

33. The method of furnace heating which naeoeoi consists in inducing electric current flow within a mass of material directly from high-frequency current flow outside the mass, as distinguished from linking the material in the mass and the outside current by transformer magnetic circuit, and additionally heating said mass by reflected radiantber, 1920. v

' HARVEY C. RENTSCIHHJER 

